Regulatory function of PP2C phosphatases in plant ion homeostasis

铵是农业土壤中普遍存在的关键营养素，其通过铵转运蛋白/恒河猴糖蛋白（AMT/Rh）家族的高亲和力转运蛋白被微生物和植物吸收。每个AMT成员的精确定位以及转录、转录后和翻译后调控有助于获得充足的铵营养。在拟南芥（Arabidopsis thalina）中，鉴定了六个AMT基因，它们分成两个不同的进化枝（AMT 1和AMT 2）并编码具有不同功能特性的转运蛋白。目前的知识表明，个体AMT的活性以复杂的互补方式进行调节。已确定通过C-末端磷酸化的变构开关调节AMT 1的活性。AMT羧基末端保守苏氨酸的磷酸化使AMT 1三聚体的转运失活。这种磷酸化直接依赖于铵，并在铵再供应后迅速增加。在项目“植物铵转运蛋白（AMT）整合调控网络”框架内的初步工作将CIPK 23鉴定为AMT 1磷酸化和调节激酶。结果进一步鉴定了两种PP 2C磷酸酶作为AMT 1转运蛋白的潜在调节剂。复杂的AMT 1调节级联作为一个整体尚未完全解码。目前尚不清楚已确定的PP 2C是否以及如何在这一级联中发挥作用。因此，这些候选人将在本项目中得到描述。这些结果将有助于更好地理解植物体内NH_4 ~+、K ~+和NO_3 ~-离子稳态的分子基础。

Ammonium is an ubiquitous key nutrient in agricultural soils that is taken up by microorganisms and plants via high-affinity transporters of the ammonium transporter / rhesus glycoprotein (AMT/Rh) family. The precise localization of each AMT member and the transcriptional, post-transcriptional and post-translational regulation contribute to the adequate ammonium nutrition. In Arabidopsis thalina, six AMT genes are identified, which separate in two distinct clades (AMT1 and AMT2) and code for transporters with distinct functional properties. Current knowledge suggests that the activity of individual AMTs is regulated in a complex, complementary manner. An allosteric switch by phosphorylation at the C-terminus has been identified that regulates the activity of AMT1s. The phosphorylation of a conserved threonine in the AMT carboxyl-terminus inactivates the transport of the AMT1 trimer. This phosphorylation is directly ammonium dependent and increases rapidly after ammonium resupply. Preliminary work in the frame of the project "Plant ammonium transporter (AMT) integration in regulatory Networks" identified CIPK23 as AMT1 phosphorylating and regulating kinase. The results further identified two PP2C phosphatases as potential regulators of AMT1 transporters. The complex AMT1 regulation cascade as a whole is not completely decoded yet. It is still unclear if and in which way the identified PP2Cs might act in this cascade. These candidates will therefore be characterized in this project. The results will yield a better comprehension of the molecular basis of NH4+, K+ and NO3- ion homeostasis in plants.